opa test --bench fails with "eval_cancel_error: caller cancelled query execution"

[anderseknert]

Expected Behavior

opa test --bench testing.rego to report the result of benchmarking a simple policy.

Actual Behavior

$ opa test --bench testing.rego
data.testing.test_allow_is_true: ERROR (5.000137933s)
  eval_cancel_error: caller cancelled query execution
--------------------------------------------------------------------------------
ERROR: 1/1

Steps to Reproduce the Problem

testing.rego

package testing

allow {
	true
}

test_allow_is_true {
	allow
}

$ opa test --bench testing.rego

Additional Info

Setting the --timeout flag to 30s provides the benchmark result. Two things stand out to me here:

1. If no explicit --timeout is provided, I believe the default should be to run until finished.
2. If a --timeout is provided and exceeded, a human readable message should be printed.

[tsandall]

I think we can fix this easily by making the timeout default dynamic. If --bench is not specified, the 5s timeout is fine (that's more than enough time a query to return). If --bench is specified, we can just crank the timeout to 30s as that would give the Go benchmark runner enough time to find a stable measurement.